1. Field of the Invention
The present invention relates to a subjective optometric apparatus and, more specifically, to a subjective optometric apparatus that the subject can wear like glasses.
2. Description of the Related Art
Conventionally, ophthalmic operators like oculists measure various refraction characteristics of the eye to be examined by using an objective refractometer and a subjective optometric apparatus such as a vision tester, and, on the basis of the refraction characteristics thus obtained, prescription values for glasses suitable for the eye, such as spherical degree S, cylindrical degree C., and axial angle A of cylinder axis, are determined.
The above-mentioned subjective optometric apparatus contains in its casing a turret with a number of lenses of different refractive powers arranged circumferentially. By rotating this turret by a predetermined angle, an arbitrary one of these lenses is selectively set in front of the eye to be examined. The operator asks the subject about the way he or she sees through the selected glass, and repeats such inquiry, successively selecting different lenses. In this way, the refraction characteristics of the eye are examined.
It is to be noted that it is not always desirable to adopt the refraction characteristics (or prescription values) thus obtained by the above-described subjective optometric apparatus as they are as the prescription values for the glass to be actually prescribed.
The prescription values obtained by this subjective optometric apparatus are determined on the basis of the results of judgments made as to whether the selected lens of the subjective optometric apparatus enable the subject to make a normal visual recognition of symbols, characters or the like on an eye chart at a distance, for example, of 5 m. That is, the refraction characteristics thus obtained are ones obtained through testing of vision with respect to an object at a distance, i.e., a so-called far vision test.
In the actual use of prescribed glasses, not only far vision but also vision for a nearby object is required as in the case of reading a newspaper at hand or checking any surface irregularity of the ground on which the user stands. When thus looking at a nearby object, an excessive adjusting performance is required of the eye. Thus, with the prescribed values obtained through the far vision test alone, the user can experience an extreme fatigue in the eye, dizziness, or headache.
Thus, it is necessary to rectify to some degree the balance between far vision and near vision. In view of this, an adjustment inspection is executed in which the subject wears a spectacle-shaped trial frame on his or her face, and in which lenses of refraction characteristics close to the prescription values are successively attached to the trial frame to make an inquiry as to the way the subject sees objects at a distance and nearby ones through these lenses to thereby determine final prescription values.
However, it takes time to thus perform far vision test and adjustment inspection, resulting in a prolonged inspection.
In view of this, the present inventors have developed a subjective optometric apparatus substantially reduced in size to make it possible to perform both far vision test and near vision test with a single apparatus.
This subjective optometric apparatus uses an Alvarez lens.
An Alvarez lens consists of two optical elements (e.g. phase plates) each of which has one surface formed in an aspherical configuration that can be expressed by the equation: x=A {(1/3) y3+yz2} and the other surface formed flat.
In arranging the two optical elements constituting the Alvarez lens, they are rotated by 180 degrees with respect to each other, with their aspherical surfaces being opposed to each other. By displacing (moving) the two optical elements in opposite directions by the same displacement amount (movement amount), a continuous variation in refractive power is realized (See U.S. Pat. No. 3,305,294).
By using this Alvarez lens instead of the turret, it is possible to achieve such a reduction in size and weight that the subject can wear the subjective optometric apparatus main body.
Incidentally, to enable the subject to wear the subjective optometric apparatus on the face as in the case of a trial frame, it is necessary to provide the earpiece members, nose pad member, etc. in the main body of the device.
In many cases, the positions of the ears, the shape and height of the nose, and the positional relationship between the ears and the nose differ from subject to subject. Thus, it is necessary for the earpiece members and the nose pad member to exhibit a certain fixed movable range to allow positional adjustment, etc.
It is to be noted, however, that in the case in which a function to adjust the positions of the earpiece members, etc. is simply provided, the operator moves his or her hand around the face of the subject during adjustment. Thus, when the adjustment of the members take time, it may give discomfort to the subject.
At the same time, a prolonged adjusting operation would be a waste of time and labor for the operator.